The present invention relates to radiation curable silicone compositions, more particularly to radiation curable silicone compositions that exhibit very rapid cure speed.
Radiation curable systems that are based on iodonium salt catalyzed epoxy-functional silicone polymers and are useful for release coating applications are well known, see, for example, coassigned U.S. Pat. No. 4,279,717.
Increasing the speed at which such systems may be cured has been a topic of great interest. One approach has been to include cure speed enhancing additives, such as for example, photosensitizers, to such compositions. Iodonium cationic photocatalysts typically exhibit peak absorption at wavelengths less than 250 nanometers (xe2x80x9cnmxe2x80x9d) and do not absorb or otherwise respond to radiation of wavelength greater than 300 nm. Thioxanthones which absorb light in the 300 to 400 nm range have been shown to be effective photosensitizers for iodonium photocatalysts in epoxysilicone-based formulations, see, for example, coassigned U.S. Pat. No. 5,650,453. Visible light photosensitizers for iodonium salt-catalyzed cationic curing systems are also known, see, for example, U.S. Pat. No. 4,250,053 and U.S. Pat. No. 4,356,050. However, the solubility of such materials in nonpolar epoxysilicone media is generally limited, so that their potential use for photocurable silicone applications is typically limited to very highly functionalized silicone polymers and monomers.
There remains a continuing interest in providing radiation curable silicone compositions that exhibit improved properties, such as for example, more rapid cure speed.
The present invention is directed to a radiation curable composition, comprising an epoxy-functional silicone polymer, a photocatalyst, and a cure speed-enhancing amount of a non-fluorescing polycyclic aromatic compound, said polycyclic aromatic compound comprising at least one hydroxyl, alkoxy or glycidyl ether substituent bonded to an aromatic carbon atom of the compound.
The composition of the present invention exhibits improved cure speed.
In a preferred embodiment, the composition of the present invention comprises, based on 100 parts by weight (xe2x80x9cpbwxe2x80x9d) of the composition, from 90 pbw to 99.9 pbw, more preferably from 95 pbw to 99.5 pbw, and still more preferably from 96 pbw to 99 pbw, of the epoxy-functional silicone polymer, from 0.05 pbw to 8 pbw, more preferably from 0.2 pbw to 5 pbw, and still more preferably from 0.5 pbw to 2 pbw, of the photocataylst and from 0.05 pbw to 2 pbw, more preferably from 0.1 pbw to 2 pbw, and still more preferably from 0.2 pbw to 1 pbw, of the non-fluorescing polycyclic aromatic compound.
Compounds suitable as the polycyclic aromatic compound of the composition of the present invention are those aromatic hydrocarbon compounds comprising two or more hydrocarbon rings, preferably at least two of which are fused rings, that is, rings joined such that each of the fused rings shares two or more carbon atoms with at least one other ring, which contain the maximum possible number of conjugated double bonds for number of carbon atoms contained in the rings and which contain at least one hydroxy, alkoxy or glycidyl ether substituent bonded to an aromatic carbon atom of the compound.
Polycyclic aromatic compounds suitable for use as the polycyclic aromatic compound of the present invention include, for example, hydroxypentalenes, hydroxyindenes, naphthols, dihydroxynaphthalenes, alkoxynaphthols, alkoxynaphthalenes, alkoxydihydoxynaphthalenes, glycidyl naphthalene ethers, hydroxyazulenes, alkoxyazulenes hydroxyphenanthrenes, alkoxyphenanthrenes, hydroxyanthracenes, alkoxyanthracenes, hydroxyanthrols and alkoxyanthrols.
In a preferred embodiment, the polycyclic aromatic compound comprises one or more compounds of the structural formula (I): 
wherein R1, R2, R3, R4, R5, R6, R7 and R8 are each independently H, halo, hydroxy or a monovalent hydrocarbon radical, provided that at least one of R1, R2, R3, R4, R5, R6, R7 and R8 is hydroxy, alkoxy or a monovalent glycidyl ether radical.
As used herein, the terminology xe2x80x9cmonovalent hydrocarbon radicalxe2x80x9d includes monovalent acyclic hydrocarbon radicals, monovalent alicyclic hydrocarbon radicals and monovalent aromatic hydrocarbon radicals.
As used herein, the terminology xe2x80x9cmonovalent acyclic hydrocarbon radicalxe2x80x9d means a monovalent straight chain or branched hydrocarbon radical, preferably containing from 2 to 20 carbon atoms per radical, which may be saturated or unsaturated and which may be optionally substituted or interrupted with one or more functional groups, such as, for example, amino, carboxyl, cyano, hydroxy, halo, mercapto, and oxy. Suitable monovalent acyclic hydrocarbon radicals include, for example, alkyl such as, for example, methyl, ethyl, sec-butyl, tert-butyl, octyl, dodecyl or stearyl; alkoxy, such as, for example, methoxy or ethoxy; hydroxyalkyl, such as, for example, hydroxyethyl or hydroxypropyl; alkenyl, such as, for example, ethenyl or propenyl; alkynyl, such as, for example, propynyl or butynyl; cyanoalkyl, such as for example, cyanomethyl or cyanoethyl; carboxyalkyl, such as, for example, carboxymethyl or carboxypropyl; alkylamido such as, for example, methylamido or dodecylamido; and haloalkyl, such as, for example, chloromethyl, 2-fluoropropyl, 2,2-difluropropyl or 3,3,3-trifluoropropyl, as well as monovalent glycidyl ether radicals. As used herein the terminology xe2x80x9cmonovalent glycidyl ether radicalxe2x80x9d means a monovalent radical containing at least one oxygen atom substituted with at least one glycidyl-containing moiety, such as, for example, glycidyloxy or glycidylalkyloxy, including, for example, glycidylethyloxy or glycidylpropyloxy.
As used herein, the terminology xe2x80x9cmonovalent alicyclic hydrocarbon radicalxe2x80x9d means a monovalent radical containing one or more saturated hydrocarbon rings, preferably containing from 4 to 10 carbon atoms per ring, per radical which may optionally be substituted on one or more of the rings with one or more functional groups, such as for example, alkyl, halo or alkylene groups, each preferably containing from 2 to 6 carbon atoms per group, and which, in the case of two or more rings, may be fused rings. Suitable monovalent alicyclic hydrocarbon radicals include, for example, cyclohexyl and cyclooctyl.
As used herein, the terminology xe2x80x9cmonovalent aromatic hydrocarbon radicalxe2x80x9d means a monovalent hydrocarbon radical containing at least one aromatic ring per radical, which may optionally be substituted on the aromatic ring with one or more functional groups, such as for example, alkyl, halo or alkylene groups, each preferably containing from 2 to 6 carbon atoms per group. In a preferred embodiment, the monovalent aromatic hydrocarbon radical is monocyclic, that is, contains only one aromatic ring per radical. Suitable monovalent aromatic hydrocarbon radicals include, for example, phenyl, tolyl, 2,4,6-trimethylpheny and 1,2-isopropylmethylphenyl.
In a preferred embodiment, at least two, more preferably, two, of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently hydroxy, alkoxy or a monovalent glycidyl ether radical.
As used herein the notation xe2x80x9c(Cx-Cy)xe2x80x9d, wherein x and y are each positive integers, in reference to an organic compound or substituent group means that the compound or substituent group may contain from x carbon atoms to y carbon atoms per compound or group.
In a preferred embodiment, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently H, hydroxy, alkyl, preferably (C1-C6)alkyl, alkoxy, preferably (C1-C6)alkoxy, a monovalent glycidyl ether radical, preferably glycidyloxy, or alkylamido, preferably (C1-C18)alkylamido, provided that at least one of R1, R2, R3, R4, R5, R6, R7 and R8 is hydroxy, alkoxy or a monovalent glycidyl ether radical.
In a highly preferred embodiment, one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently hydroxy, alkoxy, preferably (C1-C6)alkoxy, or a monovalent glycidyl ether radical, preferably glycidyloxy, and the remaining substituents are each independently H or (C1-C6)alkyl.
In a highly preferred embodiment, one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each hydroxy, at one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently alkoxy, preferably (C1-C6)alkoxy, and the remaining substituents are each independently H or alkyl, preferably (C1-C6)alkyl. Exemplary compounds include 4-methoxy-1-naphthtol, 7-methoxy-1-naphthol, dimethoxynaphthtols, 4-butoxy-1-naphthol and dibutoxynaphthols, with 1-naphthol compounds being preferred.
In a highly preferred embodiment, one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently hydroxy or alkoxy, preferably (C1-C6)alkoxy, another one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently alkylamido, preferably (C1-C18)alkylamido, and the remaining substituents are each independently H or alkyl, preferably (C1-C6)alkyl. Exemplary compounds include N-dodecyl-1-hydroxy-2-naphthalene carboxamide and N-dodecyl-1-methoxy-2-naphthalene carboxamide.
In a highly preferred embodiment, two or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each hydroxy and the remaining substituents are each independently H or alkyl, preferably (C1-C6)alkyl. Exemplary compound include 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,7-dihydroxynaphthalene and trihydroxynaphthalenes.
In a highly preferred embodiment, one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently alkoxy, preferably (C1-C6)alkoxy, and the remaining substituents are each independently H or alkyl, preferably (C1-C6)alkyl. Exemplary compounds include 1-methoxynaphthalene, dimethoxynaphthalenes, 1-butoxynaphthalene and dibutoxynaphthalenes.
In a highly preferred embodiment, one or more of R1, R2, R3, R4, R5, R6, R7 and R8 are each independently a monovalent glycidyl ether radical, preferably glycidyloxy, and the remaining substituents are each independently H or alkyl, preferably (C1-C6)alkyl. Exemplary compounds include 1-naphthyl glycidyl ether, 1,4-diglycidyl naphthalene ether, 1,5-diglycidyl naphthalene ether, 1,6-diglycidyl naphthalene ether and 2,7-diglycidyl naphthalene ether.
Epoxy-functional silicone polymers suitable as the epoxy-functional silicone polymer of the present invention are known in the art, see, for example, U.S. Pat. No. 4,279,717, and include, for example, polydimethylsiloxanes having pendant epoxy functional substituent groups, such as, for example, xe2x80x94(CH2)3xe2x80x94Oxe2x80x94CH2xe2x80x94CHCH2O or 2-ethyl-(3,4-epoxycyclohexyl), that is, xe2x80x94(CH2)C6H9O.
In a first preferred embodiment, the epoxy-functional silicone polymer comprise one or more polymers or copolymers according to the structural formula (II)
MEDEaDbMExe2x80x83xe2x80x83(II)
wherein:
ME is R92R10SiO1/2;
D is and R112SiO;
DE is R12R13SiO; each R9,R11 and R12 is independently a monovalent hydrocarbon radical; each R10 and R13 is independently alkylene epoxycycloalkyl or glycidoxyalkyl; and a and b are each independently integers from 10 to 250.
In a preferred embodiment, each R9, R11 and R12 is independently alkyl, aryl, haloalkyl or hydroxyalkyl, more preferably (C1-C6)alkyl, aryl, halo(C1-C6)alkyl or hydroxy(C1-C6)alkyl.
In a preferred embodiment, R10 and R13 are each independently 2-ethyl-(3,4-epoxycyclohexyl) or xe2x80x94(CH2)3xe2x80x94Oxe2x80x94CH2xe2x80x94CHCH2O.
In second preferred embodiment, the epoxy-functional silicone polymer comprises one or more polymers or copolymers according to the structural formula (III):
MDEcDdMxe2x80x83xe2x80x83(III)
wherein:
M is R143SiO1/2;
each R14 is independently a monovalent hydrocarbon radical,
D and DE are each defined as above, and
c and d are each independently integers from 50 to 500.
In a preferred embodiment, each R14 is independently alkyl, aryl, haloalkyl or hydroxyalkyl, more preferably (C1-C6)alkyl, aryl, halo(C1-C6)alkyl or hydroxy(C1-C6)alkyl.
In a preferred embodiment, R14 is 2-ethyl-(3,4-epoxycyclohexyl) or xe2x80x94(CH2)3xe2x80x94Oxe2x80x94CH2xe2x80x94CHCH2O.
Certain modified epoxy functional silicones have been found to allow the use of a wider range of photoinitiators and additives, that is, photoinitiators and additives that are immiscible with or only sparingly soluble in the epoxy functional silicones of structural formulas (II) and (III).
In a third preferred embodiment, the epoxy functional silicone comprises an oxo acid modified epoxy functional silicone made by reaction of an epoxy functional silicone according to formula (II) or (III) above with less than its molar equivalent, based on epoxy functionality, of one or more polyether carboxylic acids. Suitable oxo acid modified epoxy functional silicones include those made by reaction of an epoxy functional silicone with a polyether acid according to the structural formula (IV):
HOOC(((CH2)eO)f((CH2)gO)h)R15xe2x80x83xe2x80x83(IV)
wherein:
R15 is H or a monovalent hydrocarbon,
e, f, g and h are each integers xe2x89xa70, provided that, at least, e and f or g and h are each greater than 0.
In a preferred embodiment, R15 is H, alkyl, alkenyl, alkynyl aryl, alkaryl or carboxylate such as, for example, 3,6-dioxoheptanoic acid or 3,6,9-trioxodecanoic, as described in coassigned U.S. Pat. No. 5,721,290.
In a fourth preferred embodiment, the epoxy functional silicone comprises a non-fluorescing polycyclic aromatic-modified epoxysilicone polymer or copolymer made by reaction of an epoxy functional silicone polymer or copolymer according to formula (II) or (III) with less than its molar equivalent, based on epoxy functionality, of a compound selected from the group consisting of R16COOH, (R16CO)2O, R16COX, R16SO3H or R16SO2X, wherein R16 is a monovalent polycyclic aromatic hydrocarbon radical and X is halo. As used herein, the terminology xe2x80x9cmonovalent polycyclic aromatic hydrocarbon radicalxe2x80x9d means a monovalent hydrocarbon radical containing two or more fused aromatic rings per radical, which may optionally be substituted on the aromatic ring with one or more alkyl, halo or alkylene groups, each preferably containing from 2 to 6 carbon atoms per group, or other functional groups. Suitable monovalent polycylic aromatic hydrocarbon radicals include, for example, naphthyl and anthryl. Suitable compounds include, for example, naphthoic acid, 1-naphthyl acetic acid, (1-naphthoxy)acetic acid, 4-hydroxy-2-naphthylacetic acid, naphthyl-1-sulfonic acid and anthracene-9-carboxylic acid. Similar compounds and their syntheses are described in coassigned U.S. Pat. No. 5,583,195.
Suitable onium photocatalysts, such as for example, triphenylsulfonium salts, diphenyl iodonium salts, azonium salts, are generically known. Iodonium salts such as, for example, bis(4-alkylphenyl)iodonium hexafluroantimonates, or bis(4-alkylphenyl)iodonium hexaflurophosphates, are preferred due to their low toxicity and compatibility with non-polar materials.
In a preferred embodiment, the photocatalyst comprises an iodonium salt that is compatible with the other components of the radiation curable epoxysilicone composition, such as, for example, the salts disclosed in U.S. Pat. No. 4,279,717. In a more highly preferred embodiment, the photocatalyst component of the radiation curable epoxysilicone composition of the present invention comprises one or more of the alkylphenyl iodonium salts of PF6xe2x88x92, SbF6xe2x88x92 or B(C6F5)4xe2x88x92. In a highly preferred embodiment, the photocatalyst is selected from one or more of mixed bis(4-(C8-C14)alkylphenyl)iodonium hexafluoroantimonates, mixed bis(4-(C8-C14)alkylphenyl)iodonium hexafluorophosphates and (4-octyloxyphenyl)(phenyl)iodonium hexafluoroantimonate.
In a preferred embodiment, the composition of the present invention comprises an oxo acid-modified epoxysilicone polymer or copolymer, an (alkylphenyl)iodonium hexafluorophosphate photoinitiator and a cure speed enhancing amount of a polycylclic aromatic compound.
In a preferred embodiment, the composition of the present invention comprises an polycyclic aromatic-modified epoxysilicone polymer or copolymer, (4-octyloxyphenyl)(phenyl)iodonium hexafluoroantimonate and a cure speed enhancing amount of a polycylclic aromatic compound.
The radiation curable composition of the present invention may optionally include other components known in the art such as, for example, reactive or non-reactive diluents, such as, for example, aliphatic alcohols such as, for example, diacetone alcohol, oxiranyl compounds such as, for example, alkylgycidyl ethers and alkenyl compounds such as, for example, vinyl ethers; and photosensitizers, such as, for example, thioxanthones, including for example, 2-chloro-4-propoxythioxanthone and 2-isopropylthioxanthone.
A layer of the radiation curable composition of the present invention is applied to the substrate by, for example, spray coating, roll coating, rod coating or extrusion and then exposed to actinic radiation, preferably ultraviolet (xe2x80x9cUVxe2x80x9d) radiation, to cure the coating layer. Suitable substrates include for example, paper, such as, for example, supercalendered kraft paper, glassine paper, machine finished paper and machine glazed paper, polymer films, such as, for example, polyolefin films, polyester films and polystyrenic films, and metal foils, such as, for example, aluminum foil, as well as composite substrates made by combining any of the above listed substrates, such as, for example, polyolefin-coated kraft paper.
The coated substrate made by the method of the present invention is useful a release liner for pressure sensitive adhesive-backed articles such as, for example, adhesive labels and adhesives tapes.
An adhesive laminate comprises a release-coated substrate, said release-coated substrate comprising a first substrate and a cured layer of the composition of the present invention disposed on at least a portion of at least one surface of the first substrate, laminated with a pressure sensitive adhesive-coated substrate, said pressure sensitive adhesive-coated substrate comprising a layer of a pressure sensitive adhesive disposed on at least a portion of at least one surface of a second substrate, such that the cured coating layer of the release-coated substrate is in contact with the pressure sensitive adhesive layer on the pressure sensitive adhesive-coated substrate. Suitable pressure sensitive adhesive compositions, such as, for example, emulsion acrylic adhesives, solvent acrylic adhesives, hot melt adhesives, emulsion rubber adhesive, solvent rubber adhesives, and methods for making pressure sensitive adhesive coated substrates are well known in the art.
The pressure sensitive adhesive coated substrate may be easily removed from the coated substrate made by the method of the present invention and applied to another substrate, as desired.